1. Field of the Invention
This invention relates to a terminal for a piezoelectric device, and more particularly, to a terminal which has a bent contact portion or includes two separately formed, opposed contact portions and is adapted for use as, for example, an input terminal, an output terminal, an internal connecting terminal, or an earth terminal for a piezoelectric device, such as a ladder type filter.
2. Description of the Prior Art
A ladder type filter is shown in FIG. 11, by way of example, as a piezoelectric device having known terminals forming the background of this invention, including an output terminal as shown in FIG. 12. The ladder type filter 1 includes a casing 2 formed from a synthetic resin and having a bottom opening closed by a cover 3. The casing 2 contains four piezoelectric resonators 4a, 4b, 4c and 4d, and an input terminal 5a, a relay terminal 5b, an earth terminal 5c, an output terminal 5d and a spring terminal 5e for interconnecting the piezoelectric resonators 4a, 4b, 4c and 4d.
The earth terminal 5c, the output terminal 5d and one contact portion 6b of the relay terminal 5b are each formed as a bent terminal having a U-shaped cross section. Referring more specifically to the output terminal 5d, it has a substantially square base portion 5d1, as shown in FIG. 12. The base portion 5d1 has a straight leg 7d extending outwardly to define an external connector. The output terminal 5d also has a bent portion 5d2 extending parallel to its base portion 5d1 and spaced apart from the base portion 5d1 by a small distance. The base portion 5d1 has on its outer surface a protrusion 8 resiliently disposed against one principal surface of the piezoelectric resonator 4c and the bent portion 5d2 likewise has on its outer surface a protrusion 8 resiliently disposed against one principal surface of the piezoelectric resonator 4d.
Likewise, the earth terminal 5c is formed as a bent terminal having a base portion 5c1, a bent portion 5c2 and two protrusions 8. One contact portion 6b of the relay terminal 5b also has a base portion 6b1, a bent portion 6b2 and two protrusions 8. Moreover, the input terminal 5a has a protrusion 8 resiliently disposed against one principal surface of the piezoelectric resonator 4a and the other contact portion 6c has a protrusion 8 resiliently disposed against the other principal surface of the piezoelectric resonator 4d.
The ladder type filter 1 also has a plurality of sheets 9 formed of a synthetic resin, such as silicone rubber, including one sheet 9 interposed between the base portion 5d1 and the bent portion 5d2 of the output terminal 5d. The resin sheets 9 are provided for protecting the piezoelectric resonators 4a, 4b, 4c and 4d from an external shock by providing a shock absorbing force in a direction extending along a thickness of the sheets 9 and perpendicular to the opposing major surfaces of the base portion 5d1 and the bent portion 5d2 surrounding the sheet 9 as seen in FIG. 12.
However, the sheets 9 may cause problems in the filter 1 shown in FIG. 11. For example, the sheets 9 may be displaced or moved from a desired position between the bent portion and base portion of the terminals, especially if a shock or stress applied to the filter 1 is substantial. Also, although the resin sheets in the known ladder type filter 1 as described above are effective for protecting the piezoelectric resonators from a shock when the filter has been dropped or hit hard, the application of physical stress from an external source or vibration of the piezoelectric resonators per se, is likely to cause a ripple failure in the frequency and group delay characteristics of the filter. More specifically, the sheets 9 create an obstruction to oscillation or vibration between the bent portion and base portion of any terminal, in a direction that is parallel to the major surfaces of the bent portion and base portion which surround the sheets. This obstruction of vibration causes an unbalanced vibration, other than the desired piezoelectric vibration, between the piezoelectric element and the bent portion of the terminal. Consequently, a ripple failure occurs in the frequency and group delay characteristics of the filter and lowers the filter characteristic quality.
As a result of the ripple failure, or the distortion in waveform of frequency characteristics which occurs in a filter band, the group delay and phase characteristics of the filter are deteriorated. Consequently, the use of the ladder type filter in a communication system results in increasing of undesired demodulation distortion and distortion of any sound thereby received, or the appearance of bit errors in a digital communication system which causes problems in data communications.